Well cementing is a process used in penetrating subterranean formations to recover resources such as gas, oil, and minerals. Well cementing generally involves drilling a wellbore, placing a string of pipe within the wellbore, and pumping a cement slurry into the annulus, or space between the pipe and the walls of the wellbore. After the cement is allowed to set, the annulus is sealed preventing the well fluids from escaping into the formation. Although several suitable cement compositions can be used, low density or lightweight cement compositions are commonly used in wells that extend through weak formations because they can reduce the hydrostatic pressure exerted by the column. This reduction can reduce and/or eliminate formation fractures, drilling and servicing fluid loss, and damage to the formation.
A variety of lightweight cement compositions using lightweight additives and/or beads have been used in cementing. In the “dry blend” method, lightweight beads are combined with a dry bulk mixture of cement and then mixed with water to form a cement slurry. When the beads are distributed uniformly within the cement composition prior to the addition of water, the method creates an ideal lightweight cement composition. However, the dry blend method has two related problems when used in large-scale manufacturing. First, the beads often become packed during storage leading to large masses of beads or “agglomerations.” Second, the beads often segregate from the dry cement during loading, unloading, and transporting. Both problems lead to a non-uniform distribution of beads within the dry cement composition. If untreated, non-uniformities in the bead distribution can prevent a uniform cement composition. Therefore, special procedures are often employed to reduce the segregation or packing of beads before water is added to the cement composition or before the slurry is added to the wellbore. These procedures add to the complexity and increase the overall cost of the cementing process.
Several liquid methods have been proposed to address the known problems of the dry blend method with varying success. One liquid method involves suspending beads in a fluid containing water gelled with sodium bentonite or other water absorbing material. As long as the liquid-bead suspension remains flowable, this “liquid suspension” method creates an ideal liquid additive for lightweight cement compositions. However, bead packing remains an issue and once again, special procedures must be employed to re-suspend the beads that have been separated from the fluid.